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Abstract:

A metallic container closure including a shell of a thin metal sheet
having a circular top panel wall (7) and a skirt wall (9), and a
synthetic resin liner arranged in the shell, the skirt wall (9) having a
thread-forming region and an annular groove (17) positioned at an upper
end portion of the thread-forming region, wherein an internal pressure
release line A extending in the circumferential direction is arranged in
the skirt wall (9) at a portion over the annular groove (17), and annular
bead (30) is arranged so as to pass through between the internal pressure
release line A and the annular groove (17).

Claims:

1. A metallic container closure comprising a shell of a thin metal sheet
having a circular top panel wall and a cylindrical skirt wall hanging
down from a circumferential edge of the top panel wall, and a synthetic
resin liner arranged in the shell, the skirt wall of the shell having a
thread-forming region and an annular groove positioned at an upper end
portion of the thread-forming region, wherein: an internal pressure
release line inclusive of a slit extending in the circumferential
direction is arranged in the skirt wall at a portion over the annular
groove, and an annular bead is arranged so as to pass through between the
internal pressure release line and the annular groove; wherein the
annular bead extends in the horizontal direction, and wherein a knurling
is formed over the annular groove of the skirt wall and the internal
pressure release line is formed at the upper end of the knurling.

2. A metallic container closure according to claim 1, wherein the
internal pressure release line is constituted by a plurality of slits
arranged in the circumferential direction maintaining a distance, and a
low-strength bridging portion present among the slits and having a small
width in the circumferential direction so as to be broken by an elevated
pressure in a container.

3. A metallic container closure according to claim 1, wherein the
internal pressure release line is formed by one long slit extending in
the circumferential direction.

4. A metallic container closure according to claim 1, wherein an internal
pressure release assist line is formed on an extension in the
circumferential direction of the internal pressure release line, the
internal pressure release assist line being constituted by a plurality of
slits extending in the circumferential direction and a high-strength
bridging portion which is positioned among the slits and has a width in
the circumferential direction larger than that of a low-strength bridging
portion.

5. (canceled)

6. (canceled)

7. (canceled)

8. A metallic container closure according to claim 4, wherein the
plurality of slits forming the internal pressure release line and the
internal pressure release assist line all have substantially the same
width in the circumferential direction.

9. A metallic container closure according to claim 3, wherein the
internal pressure release line is constituted by the long slit having a
length 5 to 35% of the circumferential length of the skirt wall.

10. A metallic container closure according to claim 9, wherein the
internal pressure release line includes slits having a short
circumferential length in addition to the long slit.

11. A metallic container closure according to claim 1, wherein at least
one weakened line extending in an axial direction is formed in a region
where the internal pressure release line is formed.

12. A metallic container closure according to claim 11, wherein the
weakened line is extending being continuous to the slit forming the
internal pressure release line or from near the slits.

13. A metallic container closure according to claim 11, wherein the
weakened line is positioned over the slit.

14. A metallic container closure according to claim 11, wherein the
weakened line is a score.

15. A metallic container closure according to claim 11, wherein the
weakened line is formed in a portion either at an end of the internal
pressure release line in the circumferential direction or at an
intermediate portion thereof in the circumferential direction.

16. A metallic container closure according to claim 1, wherein a pair of
weakened lines extending aslant with respect to an axial direction are
formed at both ends of the internal pressure release line in the
circumferential direction, the pair of weakened lines extending in a
direction in which they approach each other or separate away from each
other from the lower side toward the upper side at slanting angles
θ in a range of 10 to 45 degrees with respect to the axial
direction.

17. A metallic container closure according to claim 16, wherein the pair
of weakened lines are extending in a direction in which they approach
each other from the lower side toward the upper side.

18. A metallic container closure according to claim 15, wherein the pair
of weakened lines are extending upward in the axial direction being
continuous to the slit or from near the slit.

19. A metallic container closure according to claim 2, wherein the
internal pressure release line is formed over an angular range of 40 to
95 degrees.

20. A metallic container closure according to claim 19, wherein the
low-strength bridging portion in the internal pressure release line has a
width of 0.5 to 0.9 mm in the circumferential direction, and the slit in
the internal pressure release line has a length of 2.5 to 4.0 mm in the
circumferential direction.

21. A metallic container closure according to claim 19, wherein the
internal pressure release line includes 4 to 6 low-strength bridging
portions.

[0003] The present invention relates to a metallic container closure
having an internal pressure release function, i.e., having a function for
automatically releasing the pressure in the container when the pressure
in the container is elevated excessively.

[0004] 2. Description of the Related Art

[0005] Usually, a carbonated beverage or the like beverage is filled in a
container, and a container closure is mounted on the mouth-and-neck
portion of the container to seal the mouth-and-neck portion. When the
content in the container is heated to an excess degree in this state,
however, the pressure in the container may elevate excessively. The
container closure may, further, be once removed from the mouth-and-neck
portion of the container and may be mounted again on the mouth-and-neck
portion of the container to seal the mouth-and-neck portion. The content
in the container, however, may often be rotten and fermented. In this
case, too, the pressure in the container may elevate to an excess degree.

[0006] When the pressure in the container is elevated as described above,
the container closure may jump off the mouth-and-neck portion of the
container or, depending upon the cases, the container itself may be
broken. To prevent such an inconvenience caused by an increase in the
pressure in the container, a metallic container closure having an
internal pressure release function has been proposed. As the metallic
container closure, there has been known the one in which an internal
pressure release line comprising a plurality of slits in the
circumferential direction and a breakable narrow bridging portions formed
among the slits, are formed at an upper end portion of a cylindrical
skirt wall that hangs down from the circumferential edge of a circular
top panel wall (see, for example, patent document 1).

[0007] With the container closure of the patent document 1, when the
pressure in the container is elevated, the bridging portions break, the
plurality of slits in the circumferential direction become continuous to
form a large slit, the gas in the container is released to the exterior
through this portion and, depending upon the cases, the top panel wall
is, at the same time, deformed like a dome to release the gas in the
container to thereby avoid inconvenience caused by an elevated internal
pressure. [0008] patent document 1: Japanese Utility Model Publication
No. 7-25318)

[0009] In the above conventional internal pressure releasing metallic
container closure, slits directed in the circumferential direction are
provided in the upper portion of the skirt wall of a shell of a thin
metal sheet, and the internal pressure release line is formed by the
slits involving a problem in that deformation takes place from the slits
that form the internal pressure release line at the time when the
container closure is mounted on the mount-and-neck portion of the
container and is wrap-seamed therewith. That is, the container closure is
wrap-seamed with the mouth-and-neck portion of the container by putting
the shell of a thin metal sheet on the mouth-and-neck portion of the
container, pushing the skirt wall of the shell onto the mouth-and-neck
portion of the container by using a suitable jig, and transferring the
shape of the outer surface (e.g., threaded shape) of the mouth-and-neck
portion of the container onto the skirt wall. When the jig is being
pushed, however, the skirt wall of the lower portions of the slits is
subject to be deformed.

[0010] In the conventional internal pressure releasing metallic container
closure, further, when the pressure in the container is suddenly and
sharply elevated, the bridging portions linking the slits in the
circumferential direction are broken over the whole circumference, and an
upper portion of the container closure inclusive of the top panel wall is
separated away from the skirt wall and jumps out.

[0011] Besides, when the shell is made of a thin metal sheet having a
tensile strength of about 195 N/mm2, the conventional internal
pressure releasing metallic container closure has been so designed that
the bridging portions among the slits are broken when the pressure in the
container is elevated to release the internal pressure. When the shell is
made of a thin metal sheet having a high tensile strength, such as a thin
plate of an aluminum base alloy having a tensile strength of 200 to 230
N/mm2, the resistance against drop impact is improved but the
bridging portions among the slits are not broken despite the pressure in
the container is elevated and the internal pressure is not released.
Therefore, the pressure in the container increases to an excess degree
still causing such inconveniences that the top panel wall of the
container closure jumps out or the container is broken.

SUMMARY OF THE INVENTION

[0012] It is therefore an object of the present invention to provide a
metallic container closure having slits that constitute an internal
pressure release line formed in an upper part of a skirt wall,
effectively preventing the skirt wall from being deformed at a portion
where the strength is decreasing due to the slits at the time of
wrap-seaming with the mouth-and-neck portion of the container.

[0013] Another object of the present invention is to provide a metallic
container closure which is capable of effectively releasing a gas in the
container while reliably preventing such an inconvenience that the
upper'portion inclusive of the top panel wall of the metallic container
closure is separated away from the skirt wall and jumps out when the
pressure is suddenly elevated in the container, and reliably prevents the
container closure from jumping out or prevents the container from being
broken when the pressure in the container is elevated.

[0014] A further object of the present invention is to provide a metallic
container closure which is capable of reliably preventing the top panel
wall from jumping out or preventing the container from being broken
despite the pressure in the container is elevated even when the container
closure is made of a thin metal sheet having a large strength.

[0015] According to the present invention, there is provided a metallic
container closure comprising a shell of a thin metal sheet having a
circular top panel wall and a cylindrical skirt wall hanging down from
the circumferential edge of the top panel wall, and a synthetic resin
liner arranged in the shell, the skirt wall of the shell having a
thread-forming region and an annular groove positioned at an upper end
portion of the thread-forming region, wherein:

[0016] an internal pressure release line inclusive of a slit extending in
the circumferential direction is arranged in the skirt wall at a portion
over the annular groove, and annular bead is arranged so as to pass
through between the internal pressure release line and the annular
groove.

[0017] In the metallic container closure of the present invention, it is
desired that the internal pressure release line:

(1) is constituted by a plurality of slits arranged in the
circumferential direction maintaining a distance, and low-strength
bridging portions present among the slits and having a small width in the
circumferential direction so as to be broken by an elevated pressure in
the container; or (2) is formed by one long slit extending in the
circumferential direction.

[0018] Further, the metallic container closure of the present invention
may preferably employ the following embodiments.

(3) An internal pressure release assist line is formed on an extension in
the circumferential direction of the internal pressure release line, the
internal pressure release assist line being constituted by a plurality of
slits extending in the circumferential direction and high-strength
bridging portions which is positioned among the slits and has a width in
the circumferential direction larger than that of the low-strength
bridging portions. (4) In addition to the internal pressure release
assist line, a fixing line comprising ultra-high-strength bridging
portions having a width in the circumferential direction larger than that
of the high-strength bridging portions is formed on an extension of the
internal pressure release line. (5) The fixing line is positioned on the
opposite side of the internal pressure release line in the direction of
diameter. (6) A reinforcing line comprising reinforcing bridging portions
having a width larger in the circumferential direction than that of the
high-strength bridging portions but is shorter in the circumferential
direction than that of the ultra-high-strength bridging portions, is
formed between the internal pressure release line and the internal
pressure release assist line. (7) The plurality of slits forming the
internal pressure release line and the internal pressure release assist
line all have substantially the same width in the circumferential
direction. (8) The internal pressure release line is constituted by long
slits having a length 5 to 35% of the circumferential length of the skirt
wall. (9) The internal pressure release line includes slits having a
short circumferential length in addition to the long slits. (10) At least
one weakened line extending in the axial direction is formed in a region
where the internal pressure release line is formed. (11) The weakened
line is extending being continuous to the slits forming the internal
pressure release line or from near the slits. (12) The weakened line is
positioned over the slits. (13) The weakened line is a score. (14) The
weakened line is formed in a portion either at an end of the internal
pressure release line in the circumferential direction or at an
intermediate portion thereof in the circumferential direction. (15) A
pair of weakened lines extending aslant with respect to the axial
direction are formed at both ends of the internal pressure release line
in the circumferential direction, the pair of weakened lines extending in
a direction in which they approach each other or separate away from each
other from the lower side toward the upper side at slanting angles
θ in a range of 10 to 4.5 degrees with respect to the axial
direction. (16) The pair of weakened lines are extending in a direction
in which they approach each other from the lower side toward the upper
side. (17) The pair of weakened lines are extending upward in the axial
direction being continuous to the slits or from near the slits. (18) The
internal pressure release line is formed over an angular range of 40 to
95 degrees. (19) The low-strength bridging portion in the internal
pressure release line has a width of 0.5 to 0.9 mm in the circumferential
direction, and the slit in the internal pressure release line has a
length of 2.5 to 4.0 mm in the circumferential direction. (20) The
internal pressure release line includes 4 to 6 low-strength bridging
portions.

[0019] According to the present invention, further, there is provided a
metallic container closure comprising a metallic shell having a circular
top panel wall made of a thin metal sheet having a tensile strength of
200 to 230 N/mm2 and a cylindrical skirt wall hanging down froth the
circumferential edge of the top panel wall, and a synthetic resin liner
arranged in the shell, the skirt wall of the shell having a
thread-forming region and an annular groove positioned at an upper end
portion of the thread-forming region, wherein:

[0020] an internal pressure release line extending in the circumferential
direction at an angle of 40 to 95 degrees is arranged in the skirt wall
at a portion over the annular groove, the internal pressure release line
being constituted by a plurality of slits arranged in a circumferential
direction maintaining a distance and low-strength bridging portions
present among the slits and having a small width in the circumferential
direction so as to be broken by an elevated pressure in the container.

[0021] The metallic container closure formed by using a thin metal sheet
of a high tensile strength may preferably employ the following
embodiments.

(21) The low-strength bridging portion in the internal pressure release
line has a width of 0.5 to 0.9 mm in the circumferential direction, and
the slit in the internal pressure release line has a length of 2.5 to 4.0
mm in the circumferential direction. (22) The internal pressure release
line includes 4 to 6 low-strength bridging portions. (23) A fixing line
is formed over an angle of 25 to 180 degrees in the portion on the
opposite side of the internal pressure release line in the direction of
diameter on an extension thereof, the reinforcing lines are formed over
an angle of 10 to 55 degrees neighboring both ends of the internal
pressure release line in the circumferential direction, the internal
pressure release assist line is formed between the reinforcing line and
the fixing line, the internal pressure release assist line being
constituted by a plurality of slits extending in the circumferential
direction and high-strength bridging portions positioned among the slits
and having a width in the circumferential direction larger than that of
the low-strength bridging portions, the fixing line being constituted by
ultra-high-strength bridging portions having a width in the
circumferential direction larger than that of the high-strength bridging
portions, and the reinforcing line being constituted by reinforcing
bridging portions having a width larger in the circumferential direction
than that of the high-strength bridging portions but is shorter in the
circumferential direction than that of the ultra-high-strength bridging
portions. (24) The fixing line is formed over an angle of 25 to 180
degrees in the portion on the opposite side of the internal pressure
release line in the direction of diameter on an extension thereof, and
the internal pressure release assist line is formed between the internal
pressure release line and the fixing line, the internal pressure release
assist line being constituted by a plurality of slits extending in the
circumferential direction and high-strength bridging portions positioned
among the slits and having a width larger in the circumferential
direction than that of the low-strength bridging portions, and the fixing
line being constituted by the ultra-high-strength bridging portions
having a width larger in the circumferential direction than that of the
high-strength bridging portions.

[0022] According to the present invention, there is further provided a
metallic container closure comprising a shell of a thin metal sheet
having a circular top panel wall and a cylindrical skirt wall hanging
down from the circumferential edge of the top panel wall, and a synthetic
resin liner arranged in the shell, the skirt wall of the shell having a
thread-forming region and an annular groove positioned at an upper end
portion of the thread-forming region, wherein:

[0023] an internal pressure release line inclusive of a slit extending in
the circumferential direction is arranged in the skirt wall at a portion
over the annular groove, and at least one weakened line extending in a
axial direction or extending aslant with respect to the axial direction
is formed in the region where the internal pressure release line is
formed.

[0024] In the metallic container closure of the invention, it is desired
that:

(25) the weakened lines are provided at both end portions of the internal
pressure release line in the circumferential direction, the pair of
weakened lines extending aslant in a direction in which they approach
each other or separate away from each other from the lower side toward
the upper side at slanting angles θ in a range of 10 to 45 degrees
with respect to the axial direction.

[0025] In the container closure of the present invention, the internal
pressure release line constituted by a slit is formed in the skirt wall
to release the internal pressure sufficiently reliably when the pressure
is excessively elevated in the container. Further, the annular bead is
arranged in the skirt wall so as to pass through between the internal
pressure release line and the annular groove making it possible to
effectively prevent the skirt wall from being deformed at a portion where
the internal pressure release line is formed at the time when the
container closure is being wrap-seamed with the mouth-and-neck portion of
the container.

[0026] In the container closure of the present invention, further, when
the weakened line extending in the axial direction is formed in the
region where the internal pressure release line is formed [embodiments
(10) to (14) described above], the skirt wall easily and quickly deforms
so as to expand outward with the weakened line as a fulcrum when the
pressure in the container is suddenly elevated. As a result, the internal
pressure release line is greatly opened to form a large opening, and the
gas is released. That is, a large opening for releasing the gas is formed
in only the region where the internal pressure release line is formed
reliably preventing such an inconvenience that the upper portion of the
container closure inclusive of the top panel wall is separated away from
the skirt wall and jumps out. Further, the gas in the container can be
reliably released.

[0027] In particular, when the pair of weakened lines extending aslant at
predetermined angles (10 to 45 degrees) with respect to the axial
direction are provided at both ends in the circumferential direction of
the internal pressure release line [embodiments (16) and (17) described
above], a very great advantage is obtained preventing such an
inconvenience that part of the container closure inclusive of the top
panel wall is separated away from the skirt wall and jumps out as
compared to when the weakened line is extending in the vertical direction
(axial direction).

[0028] That is, when the pressure in the container is abnormally elevated,
the pair of weakened lines extending in the vertical direction (i.e., in
parallel with the axial direction) may often break so as to spread along
the circumferential edge of the top panel wall (boundary portion between
the skirt wall and the top panel wall) starting from the upper end
thereof. In particular, when the internal pressure release assist line in
which the plurality of slits are extending in the circumferential
direction via the bridging portions, is provided in a portion of the
skirt wall other than the internal pressure release line, the weakened
line may often break progressively up to the bridging portions among the
slits of the internal pressure release assist line. As a result of the
breakage of the weakened line, part of the container closure inclusive of
the top panel wall may often be separated away from the skirt wall and
may jump out (hereinafter often called top panel jumping).

[0029] When the pair of weakened lines are extending aslant with respect
to the axial direction at a predetermined slanting angle θ,
however, it is made possible to effectively avoid such an inconvenience
that the weakened lines break beyond the internal pressure release line
and, hence, to reliably avoid the problem of top panel jumping.

[0030] Though the reason has not yet been clarified why provision of the
weakened lines aslant with respect to the axial direction increases the
effect for suppressing the top panel jumping, the present inventors
presume in a manner as described below. That is, when the pair of
weakened lines extend aslant in a direction in which they approach each
other from the lower side toward the upper side, the breakage thereof is
less likely to spread to the internal pressure release assist line than
when the weakened lines are extending in the vertical direction (i.e., in
parallel with the axial direction), which is convenient for preventing
the top panel jumping. Further, when the pair of weakened lines are
extending in a direction in which they separate away from each other from
the lower side toward the upper side, it is presumed that the breakage
occurs most easily and quickly proceeds releasing the inner pressure in
an early time and, as a result, the cap becomes little likely to jump.

[0031] It is important that the slanting angle θ of the weakened
lines is in a range of 10 to 45 degrees. When this angle is smaller than
10 degrees, there is no much difference from when the weakened lines are
formed in the vertical direction (i.e., in parallel with the axial
direction) easily arousing a problem of top panel jumping. When the
slanting angle θ is not smaller than 45 degrees, on the other hand,
the weakened lines are not easily broken making it difficult to release
the gas despite of an abnormal increase in the pressure in the container.
That is, even when the pressure in the container is abnormally elevated,
the weakened lines are not easily broken. Therefore, the pressure in the
container is not released despite the bridging portions are broken among
the slits in the circumferential direction. In this case, the pressure in
the container increases to a conspicuous degree, the breakage proceeds
over the whole circumference of the top panel wall of the container
closure, and the top panel wall may jump off the mouth portion of the
container (hereinafter often called top panel jumping). That is, in the
present invention, the aslant weakened lines are formed at both ends of
the internal pressure release region in a manner that the slanting angle
θ is 10 to 45 degrees to reliably avoid the problem of top panel
jumping. Further, the gas is effectively released when the pressure in
the container is abnormally elevated avoiding the inconvenience of cap
jumping.

[0032] Here, the pair of weakened lines may be so formed as to extend in a
direction in which they approach each other from the lower side toward
the upper side or, conversely, may be so formed as to extend in a
direction in which they separate away from each other from the lower side
toward the upper side. From the standpoint of reliably avoiding the above
problem of top panel jumping, it is desired that the pair of weakened
lines are extending in a direction in which they approach each other from
the lower side toward the upper side. In this case, even if the breakage
of the weakened lines spreads onto the extensions thereof, it is little
likely that the breakage spreads to other regions (e.g., to the internal
pressure release assist line) exceeding the internal pressure release
line, which is convenient from the standpoint of preventing the top panel
jumping.

[0033] Further, when the container closure is formed by using a thin metal
sheet (e.g., thin aluminum base alloy sheet) having a tensile strength of
200 to 230 N/mm2 according to the present invention, it is desired
that the internal pressure release line constituted by the plurality of
slits arranged in the circumferential direction maintaining a distance
and the low-strength bridging portions among them, has a width in a range
of 40 to 95 degrees in the circumferential direction. When the internal
pressure release line is formed in this angular range, not only an
excellent resistance against drop impact is exhibited but also a large
opening is formed being limited in the internal pressure release line due
to an elevated pressure in the container reliably preventing the
inconveniences of top panel jumping and breakage of the container.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 is a half-sectional side view of a preferred example of a
container closure of the present invention;

[0035]FIG. 2 is a half-sectional side view illustrating a state where the
container closure of FIG. 1 is put on the mouth-and-neck portion of a
container;

[0036] FIG. 3 is a sectional view illustrating, on an enlarged scale, a
major portion of the container closure in the state of FIG. 2 together
with the mouth-and-neck portion of the container;

[0037] FIG. 4 is a view illustrating a step of wrap-seaming the container
closure of FIG. 1 with the mouth-and-neck portion of the container;

[0038]FIG. 5 is a view illustrating major portions of FIG. 4 on an
enlarged scale;

[0039] FIG. 6 is a half-cut side view illustrating a state where the
container closure of FIG. 1 is wrap-seamed with the mouth-and-neck
portion of the container;

[0040]FIG. 7 is a sectional view illustrating, on an enlarged scale,
major portions of the container closure in the state of FIG. 6;

[0041]FIG. 8 is an expansion view of a skirt wall illustrating a pattern
of slits formed in the skirt wall of the container closure of FIG. 1;

[0042]FIG. 9 is an expansion view of a skirt wall illustrating another
pattern of slits formed in the skirt wall of the container closure of the
present invention;

[0043]FIG. 10 is a side view illustrating a state where the container
closure of FIG. 1 which is of the type having a weakened line in the
axial direction formed in the region of internal pressure release line,
is wrap-seamed with the mouth-and-neck portion of the container;

[0044] FIG. 11 is a view illustrating a state where the container closure
of FIG. 10 is deformed by an elevated internal pressure;

[0045] FIG. 12 is a side view illustrating a state where the container
closure having-a weakened line in the axial direction formed for an
internal pressure release line constituted by a slit in the
circumferential direction, is wrap-seamed with the mouth-and-neck portion
of the container;

[0046] FIG. 13 is a view illustrating a state where the container closure
of FIG. 12 is deformed by an elevated internal pressure;

[0047] FIG. 14 is a side view illustrating a state where the container
closure forming a weakened line in the axial direction in a pattern
different from that of FIG. 10, is wrap-seamed with the mouth-and-neck
portion of the container;

[0048] FIG. 15 is a view illustrating a state where the container closure
of FIG. 14 is deformed by an elevated internal pressure;

[0049] FIG. 16 is a side view illustrating a state where the container
closure of FIG. 1 of the type forming weakened lines aslant with respect
to the axial direction in the region of the internal pressure release
line, is wrap-seamed with the mouth-and-neck portion of the container;

[0050]FIG. 17 is a view illustrating a state where the container closure
of FIG. 16 wrap-seamed with the mouth-and-neck portion of the container
is deformed by an elevated internal pressure;

[0051] FIG. 18 is a side view illustrating a state where the container
closure forming weakened lines aslant with respect to the axial direction
in a pattern different from that of FIG. 16, is wrap-seamed with the
mouth-and-neck portion of the container;

[0052] FIG. 19 is a view illustrating a state where the container closure
of FIG. 18 wrap-seamed with the mouth-and-neck portion of the container
is deformed by an elevated internal pressure;

[0053]FIG. 20 is a side view illustrating a state of before the container
closure having weakened lines formed aslant with respect to the axial
direction for an internal pressure release line constituted by a slit in
the circumferential direction, is wrap-seamed with the mouth-and-neck
portion of the container; and

[0054] FIG. 21 is a view illustrating a state where the container closure
of FIG. 21 wrap-seamed with the mouth-and-neck portion of the container
is deformed by an elevated internal pressure.

DETAILED DESCRIPTION OF THE INVENTION

[0055] Referring to FIG. 1, the container closure of the invention
generally designated at 1 is constituted by a shell 3 of a thin metal
sheet and a synthetic resin liner 5.

[0056] There is no limitation on the material of the thin metal sheet
forming the shell 3 so far as a suitable degree of strength is
maintained, and there may be used a thin metal sheet such as of aluminum
or an aluminum alloy. From the standpoint of maintaining a particularly
excellent resistance against the drop impact, however, it is desired to
use a thin aluminum base alloy sheet having a thickness of, for example,
about 0.22 to about 0.26 mm and a tensile strength in a range of 200 to
230 N/mm2. Further, the shell 3 has a circular top panel wall 7 and
a skirt wall 9 of nearly a cylindrical shape hanging down from the
circumferential edge of the top panel wall 7.

[0057] As will be clear from FIG. 1, the lower end of the skirt wall 9 is
swollen outward in the radial direction, and a tamper-evidence (TE) hem
portion 13 is continuing to the swollen lower end portion via a plurality
of bridges 11 that can be broken.

[0058] Nearly central portion of the skirt wall 9 is serving as a
thread-forming region 15 where a thread will be formed by the
wrap-seaming that will be described later, and an annular groove 17 is
formed in an upper end of the thread-forming region 15. The annular
groove 17 is for introducing a jig used for the wrap-seaming.

[0059] A knurling 19 having recessed portions 19a and protruded portions
19b alternately arranged in the circumferential direction is formed over
the annular groove 17, and a number of slits 20 extending in the
circumferential direction maintaining a distance in the circumferential
direction are formed at the upper ends of the recessed portions 19a (near
the corners continuous to the circular top panel wall 7). A region such
as an internal pressure release line A is formed by the slits 20.
Usually, protruded portions 19b of the knurling 19 are positioned at the
portions among the number of slits 20.

[0060] If briefly described, the container closure 1 is put on the
mouth-and-neck portion 70 of the container as shown in FIGS. 2 and 3, are
wrap-seamed with the mouth-and-neck portion 70 of the container through
wrap-seaming steps shown in FIGS. 4 and 5, and is fixed to the
mouth-and-neck portion 70 of the container as shown in FIGS. 6 and 7 to
thereby seal the mouth-and-neck portion 70 of the container.

[0061] Reverting to FIG. 1, the liner 5 is formed by using a suitable
synthetic resin such as a soft polyethylene, and is desirably formed by
feeding a molten synthetic resin onto the inner surface of the top panel
wall 7 and press-forming the melt into a desired shape. The liner 5 in
the illustrated embodiment is constituted by a relatively thin circular
central portion 5a and a relatively thick annular circumferential edge
portion 5b. As will be understood from FIG. 1, the central portion of the
annular circumferential edge portion 5b is slightly recessed.

[0062] Referring to FIG. 2, the mouth-and-neck portion 70 of the container
is made of a metal, a glass or a hard resin. FIG. 2 illustrates the one
made of a metal. A curl portion 71 is formed at the upper end of the
mouth-and-neck portion 70 of the container, a thread 73 is formed in the
side surface thereof, and a jaw portion 75 is formed under the thread 73.

[0063] Referring to FIGS. 2 and 3 which are enlarged views illustrating
major portions, in a state where the container closure 1 is put on the
mouth-and-neck portion 70 of the container for being wrap-seamed with the
mouth-and-neck portion 70 of the container, the recessed portion in the
annular circumferential portion 5b of the liner 5 faces the upper end
(curled portion 71) of the mouth-and-neck portion 70 of the container,
and the lower end of the TE hem portion 13 of the container closure 1 is
positioned under the jaw portion 75 of the neck-and-mouth portion 70 of
the container.

[0064] In the above state, the wrap-seaming is effected as shown in FIGS.
4 and 5 which are enlarged views of major portions. Namely, the container
closure 1 put on the mouth-and-neck portion 70 of the container is pushed
onto the upper end of the mouth-and-neck portion 70 of the container by
using an outer push fitting 77, a thread-forming roller 79 is introduced
into the annular groove 17 in the container closure 1 while deforming the
shoulder portion thereof and, thereafter, the roller 79 is turned along
the thread 73 of the mouth-and-neck portion 70 of the container while
pressing the skirt wall 9 of the container closure 1 to thereby form, in
the thread-forming region 15 of the skirt wall 9, a thread 23 that
screw-engages with the thread 73 of the mouth-and-neck portion 70 of the
container. The lower end of the TE hem portion 13 of the container
closure 1 is pressed onto the lower side of the jaw portion 75 of
mouth-and-neck portion 70 of the container by a hem wrap-seaming roller
81, and is deformed along the lower side of the jaw portion 75.

[0065] Referring to FIGS. 6 and 7 which are enlarged views of major
portions, through the above step of wrap-seaming, the container closure 1
is fixed by wrap-seaming to the mouth-and-neck portion 70 of the
container, and the annular circumferential edge portion 5b of the liner 5
is intimately adhered to the upper end and the outer peripheral portion
of the mouth-and-neck portion 70 (curling portion 71) of the container to
seal the mouth-and-neck portion 70 of the container. In this state, the
skirt wall 9 of the container closure 1 is screw-engaged with the outer
surface of the mouth-and-neck portion 70 of the container, and the lower
end of the TE hem portion 13 of the container closure 1 is fixed to the
lower side of the jaw portion 75 of the mouth-and-neck portion 70 of the
container.

[0066] As shown in FIGS. 6 and 7, when turned in a direction of opening
the cap, the container closure 1 fixed by wrap-seaming to the
mouth-and-neck portion 70 of the container has its skirt wall 9 lifted up
and removed from the mouth-and-neck portion 70 of the container. Here,
the TE hem portion 13 has its lower end engaged with the lower side of
the jaw portion 75 of mouth-and-neck portion 70 of the container and is
limited from being lifted up. As a result, the bridges 11 break and the
TE hem portion 13 is cut away from the skirt wall 9. Therefore, the
container closure 1 removed from the mouth-and-neck portion 70 of the
container has the TE hem portion 13 that is separated, from which the
fact of unsealing can be recognized. The knurling 19 works to prevent the
slipping at the time of turning the container closure 1.

[0067] In the container closure 1 of the above constitution, the internal
pressure release line A is formed by the slits 20 and low-strength
bridging portions 50a of a short length among the slits 20 (see, for
example, FIGS. 1 and 6). That is, when the pressure in the container is
elevated due to some reason (e.g., fermentation of the content in the
container), the top panel wall 7 of the container closure 1 will swell
causing the low-strength bridging portions 50a among the slits 20 in the
internal pressure release line A to be readily broken, and the gas is
released. This effectively prevents such inconveniences that the
container closure 1 (top panel wall 7) is deformed excessively and the
cap jumps off the mouth-and-neck portion 70 of the container.

[0068] However, when the above slits 20 and the internal pressure release
line A are formed, the lower portions of slits 20 (recessed portions 19a
of knurling 19) are pulled in the step of wrap-seaming of FIG. 4, the
low-strength bridging portions 50a among the slits 20 are broken, and the
sealing becomes defective. That is, in the step of wrap-seaming, the
thread-forming region 15 in the skirt wall 9 is deformed by using the
thread-forming roller 79 along the thread 75 of the mouth-and-neck
portion 70 of the container, causing a great deformation to the portions
on the lower side of the slits 20 (recessed portions 19a) close to the
annular groove 17 into which the roller 79 is introduced.

[0069] In order to prevent the above inconvenience according to the
present invention, an annular bead 30 is arranged neighboring the upper
part of the annular groove 17 as shown in FIGS. 1 to 7 (see,
particularly, FIG. 5 which is an enlarged view). That is, formation of
the annular bead 30 prevents the deformation due to pushing by the roller
19 from transmitted upward despite the wrap-seaming is effected by
introducing the thread-forming roller 19 into the annular groove 17 as
shown in FIGS. 4 and 5. Therefore, the portion (recessed portion 19a) on
the lower side of the slits 20 is effectively prevented from being
deformed making it possible to effectively suppress the breakage of the
low-strength bridging portions 50a among the slits 20 caused by the
deformation at the time of wrap-seaming.

[0070] In the invention described above, the number of slits 20 arranged
in the circumferential direction can be formed in a variety of patterns
and part of the region therein can be used as the internal pressure
release line A.

[0071] In the example shown in FIG. 1, for example, the internal pressure
release line A constituted by low-strength bridging portions 50a having a
short length among the slits 20 is formed in an arcuate shape. Referring
to FIG. 8, on the other hand, the reinforcing line B, internal pressure
release assist line C and fixing line D are formed in this order on an
extension in the circumferential direction of the internal pressure
release line A.

[0072] As described already, the internal pressure release line A is a
region where the low-strength bridging portions 50a are formed having a
relatively short length among the plurality of slits 20, and can be
easily broken by an increase in the pressure in the container. That is,
the low-strength bridging portions 50a are readily broken as the top
panel wall 7 is deformed by an elevated pressure in the container, and
the gas is most easily released. In the internal pressure release line A,
it is desired that the low-strength bridging portions 50a have a length
(distance among the slits 20) which is, usually, in a range of 0.5 to 0.9
mm and, preferably, 0.60 to 0.85 mm. In this region, further, it is
desired that the slit 20 has a length in the circumferential direction
which is in a range of 2.0 to 5 mm and, particularly, 2.5 to 4.0 mm. When
the shell 3 is formed by using a thin metal sheet (e.g., an aluminum base
alloy) having a particularly large tensile strength, the internal
pressure release line A is formed over an angular range of 40 to 95
degrees from the standpoint of smoothly releasing the gas when the
pressure is elevated in the container though it may vary depending upon
the material of the shell 3 and the tensile strength.

[0073] The internal pressure release assist line C is constituted by
intermediate-strength bridging portions 50c which are longer than the
above low-strength bridging portions 50a among the plurality of slits 20.
The internal pressure release assist line C is a region that maintains a
state where the cap does not jump out so far as the skirt wall 9 is
screw-engaged with the mouth-and-neck portion 70 of the container despite
the pressure in the container is elevated, and so works that the gas can
be easily released in the initial state of cap-opening operation. When
the shell 3 is formed by using a thin metal sheet having a particularly
high tensile strength, the intermediate-strength bridging portions 50c in
the region C has a width in the circumferential direction in a range of
1.0 to 3.0 mm and, particularly, 1.2 to 2.5 mm. The slits 20 in the
internal pressure release assist line C have a length in the
circumferential direction of about 1.5 to about 3.5 mm.

[0074] Further, the reinforcing line B formed between the internal
pressure release line A and the internal pressure release assist line C
is for preventing the low-strength bridging portions 50a in the internal
pressure release line A from breaking progressively at one time up to the
internal pressure release assist line C (intermediate-strength bridging
portions 50c). No slit 20 is formed in the reinforcing line B. The length
of the reinforcing line B in the circumferential direction corresponds to
the bridging portion (high-strength bridging portion) 55 between the slit
20 at an end of the internal pressure release line A and the slit 20 at
an end of the internal pressure release assist line C, is longer than the
intermediate-strength bridging portion 50c described above, and is,
usually, about 5 to about 25 mm though it may vary depending upon the
diameter of the container closure 1 (diameter of the top panel wall 7).

[0075] The fixing line D, too, is a region without slit 20 and has a
length in the circumferential length which is greater than that of the
reinforcing line B (high-strength bridging portion 55), and corresponds
to the distance (ultra-high-strength bridging portion) 57 between the
slits 20 which are positioned between the ends of the internal pressure
release lines C. The fixing line D is the ultra-high-strength region. By
suitably forming these regions, it is allowed to adjust the strength
making it possible to reliably prevent such an inconvenience that the
container closure 1 jumps off the mouth-and-neck portion 70 of the
container (cap jumps out) even when the internal pressure is abruptly
elevated in the container. The position and the circumferential length of
the fixing line D (ultra-high-strength bridging portion 57) may be so set
that the gas release function of the internal pressure release line A is
not impaired when the pressure is elevated in the container. Usually, it
is desired that the fixing line D is positioned on the opposite side in
the direction of diameter of the top panel wall 7 with respect, for
example, to the internal pressure release line A from the standpoint of
balance between the gas release function and the strength. The length
thereof in the circumferential direction may differ depending upon the
material of the shell 3 and the tensile strength and is not particularly
limited, but is in a range of 25 to 180 degrees and, particularly, 40 to
90 degrees when the shell 3 is formed by using a thin metal sheet of a
particularly high tensile strength.

[0076] In the present invention, the slits 20 forming the internal
pressure release line A can be arranged in a variety of patterns.

[0077] In a pattern of FIG. 8 employed for the container closure of FIG.
1, for example, the slits 20 are arranged in the circumferential
direction so as to form various regions in the following pattern.

[0078] B-A-B-C-D-C

[0079] (A: internal pressure release line, B: reinforcing line,

[0080] C: internal pressure release assist line, D: fixing line)

[0081] The above pattern is a representative example, as a matter of
course, and the following pattern may be employed as shown, for example,
in FIG. 9 without forming the reinforcing line B.

[0082] A-C-D-C

[0083] In the present invention, further, the plurality of slits 20
forming the above-mentioned internal pressure release line A and the
internal pressure release assist line C may all have the same length in
the circumferential direction.

[0084] In the above example, further, the internal pressure release line A
is formed by a plurality of short slits 20 and breakable bridging
portions 50a. However, the internal pressure release line A can also be
formed by using only those slits having a large circumferential length.
With the internal pressure release line A formed by using only those
slits having a large circumferential length, the gas can be released when
the internal pressure is elevated without causing the bridging portions
among the slits to be broken. In this case, it is desired that the
circumferential length of the long slits is 5 to 35% of the
circumferential length of the skirt wall. Further, the slits having a
large circumferential length and the internal pressure release assist
line C formed by the above-mentioned many short slits 20, may be combined
with the above-mentioned reinforcing line B or with the fixing line D.
When there is provided the internal pressure release line A formed by the
slits having large circumferential length, however, the resistance
against drop impact decreases.

[0085] In the present invention described above, formation of the annular
bead 30 effectively prevents the lower portion of the slits 20 from being
deformed at the time of wrap-seaming, making it possible to effectively
prevent the breakage of the region where the internal pressure release
line A (particularly, low-strength bridging portions 50a) is formed at
the time of wrap-seaming and, hence, to effectively utilize the gas
releasing function of the internal pressure release region A. That is,
with the conventional container closure without the annular bead 30, when
there are formed bridging portions having a short width among the slits
in the circumferential direction, these portions tend to be broken at the
time of wrap-seaming. Therefore, the bridging portions must have an
increased width in the circumferential direction to enhance the strength,
posing limitation on the gas releasing function when the internal
pressure is elevated. The present invention, however, is free from the
above limitation.

[0086] Upon adjusting the arrangement and size of the regions such as the
internal pressure release region A to lie in the above-mentioned
predetermined range by arranging the slits 20 in the circumferential
direction, further, an excellent gas releasing function can be maintained
relying upon the internal pressure release line even when the shell 3 is
formed by using a thin metal sheet such as of an aluminum base alloy
having a tensile strength in a range of 200 to 230 N/mm2 enhancing
the resistance against drop impact and effectively preventing the top
panel jumping or the breakage of the container when the pressure in the
container is elevated.

[0087] In the present invention, further, a weakened line extending in the
axial direction can be provided in a region where the internal pressure
release line A is formed to further enhance the gas releasing function.
FIGS. 10 to 15 illustrate examples of the container closures of when the
above weakened line is provided.

[0088] For example, the container closure shown in FIG. 10 has the same
structure as the container closure 1 shown in FIG. 6 except that weakened
lines 60 extending in the axial direction (i.e., in the vertical
direction) are formed at both ends and in the central portion of the
internal pressure release line A. The weakened lines 60 may be scores or
slits formed in the outer surface side or in the inner surface side of
the skirt wall 9, or may be the slits that are formed in a perforated
manner. Upon providing the weakened lines 60, stress concentrates in the
weakened lines when the pressure in the container is suddenly elevated
causing the low-strength bridging portions 50a among the slits 20
extending in the circumferential direction to be broken and, at the same
time, quickly deforming the skirt wall 9 outward with the weakened lines
60 as fulcrums. As a result, as shown in FIG. 11, a large opening 61 of
the shape of a beak is formed in the region where the internal pressure
release line A is formed, and the gas is quickly released through the
opening 61.

[0089] Without the above weakened lines 60, when the pressure in the
container is suddenly elevated to a conspicuous degree, the low-strength
bridging portions 50a break consecutively in the circumferential
direction, i.e., the breakage spreads exceeding the internal pressure
release line A. Therefore, when the slits 20 are formed over the whole
circumference, all of the slits 20 become continuous. As a result, though
it rarely happens, the portion over the slits 20 inclusive of the top
panel wall 7 of the metallic container closure 1 is separated away from
the skirt wall 9 and jumps out. Upon forming the weakened lines 60 on the
other hand, the breakage of the low-strength bridging portions 50a is
confined within the internal pressure release line A owing to the
deformation of the skirt wall 9 with the weakened lines 60 as fulcrums.
When the pressure in the container is suddenly elevated to a conspicuous
degree, therefore, the gas is effectively released while reliably
preventing the upper part of the container closure 1 from jumping out.

[0090] In the present invention as shown in FIG. 10, it is desired that
the weakened lines 60 are continuous to the slits 20 in the internal
pressure release line A from the standpoint of deforming the skirt wall 9
with the weakened lines 60 as fulcrums. The weakened lines 60, however,
may be formed near the slits 20 so far as there takes place the above
deformation. In the above example, further, the weakened lines 60 are
arranged on the upper side of the slits 20. However, the weakened lines
60 may be arranged on the lower side of the slits 20 or may be formed on
both the upper side and the lower side of the slits 20.

[0091] The weakened lines 60 may be formed in a number of only one or in a
plural number in the internal pressure release line A. For example, the
weakened line 60 may be formed at either one or both of the ends in the
circumferential direction of the internal pressure release line A, or may
be formed in a number of at least one in a portion between both ends of
the internal pressure release line A in the circumferential direction. In
the example of FIG. 10, the weakened lines 60 are provided at both ends
of the internal pressure release line A in the circumferential direction
and, another weakened line 60 is provided in a portion between the two
ends of the internal pressure release line A in the circumferential
direction.

[0092] In the example of FIG. 10, further, the internal pressure release
line A is constituted by a plurality of slits 20 and low-strength
bridging portions 50a among them. As shown in FIG. 12, however, the
internal pressure release line A may be formed by one slit 20a which is
elongated in the circumferential direction, and weakened lines 60
described above may be formed at both ends of the slit 20a. In this case,
too, the skirt wall 9 quickly deforms when the pressure in the container
is excessively elevated, and a large opening 61 is formed in the region
where the internal pressure release line A (long slit 20a) is formed as
shown in FIG. 13 to quickly release the gas.

[0093] In this case, however, the strength against the drop impact
decreases with an increase in the length of the slit 20a. It is therefore
desired that the internal pressure release line A (slit 20a) has a length
in a range of 10 to 55 degrees and, particularly, 15 to 40 degrees.

[0094] In an example of FIG. 14 like in FIG. 10, the internal pressure
release region line A is constituted by a plurality of slits 20 and the
low-strength bridging portions 50a among them. Here, however, the
weakened lines 60 are formed at both ends of the internal pressure
release line A, and a plurality of (three) weakened lines 60 are formed
in the portions between them. In this case, a very large opening 61 of a
shape as shown in FIG. 15 is formed in the internal pressure release line
A.

[0095] In the present invention, further, the weakened lines aslant in the
axial direction may be provided at both ends of the internal pressure
release line A to further enhance the gas releasing function. FIGS. 16 to
21 show container closures provided with the weakened lines that are
aslant.

[0096] In the container closure of FIG. 16, for example, weakened lines
(hereinafter called inclined weakened lines) 63, 63 aslant in the axial
direction are provided at both ends of the internal pressure release line
A instead of forming the weakened lines 60 in the axial direction
described above. The aslant weakened lines 63 may be scores, slits or
perforations like the weakened lines 60 in the axial direction described
above, and their ends may be continuous to the slits 20 positioned at the
ends of the internal pressure release line A or may be located near the
slits 20.

[0097] Upon providing the aslant weakened lines 63, too, stress
concentrates in the aslant weakened lines 63 when the pressure in the
container is suddenly elevated causing the low-strength bridging portions
50a among the scores 20 to be broken and, at the same time, quickly
deforming the skirt wall 9 outward with the aslant weakened lines 63 as
fulcrums. As a result, as shown in FIG. 17, a large opening 65 of the
shape of a beak is formed in the internal pressure release region A,
effectively preventing the cap and the top panel from jumping out.

[0098] In the example of FIG. 16, further, the pair of aslant weakened
lines 63 are provided in a manner to approach each other toward the upper
side. Here, it is important that the slanting angle θ is set to lie
in a range of 10 to 45 degrees. That is, when the pair of aslant weakened
lines 63 are extending at the above slanting angle θ, the breakage
that takes place does not spread to the circumferential edge of the top
panel wall 7 since the weakening lines are headed toward the central
portion away from the circumferential edge of the top panel wall 7 in
contrast with the weakened lines 60 extending in the axial direction.
Therefore, the top panel jumping is more effectively avoided.

[0099] When, for example, the slanting angle θ is smaller than the
above range, it may happen that the breakage spreads from the upper ends
of the aslant weakened lines 63 to the circumferential edge of the top
panel wall 7 in case the pressure in the container is abnormally elevated
and the breakage of the aslant weakened lines 63 proceeds at one time.
That is, the breakage proceeds along the upper portion of the reinforcing
line B (high-strength bridging portions 55), and may reach the
intermediate-strength bridging portions 50c in the internal pressure
release assist line C neighboring the reinforcing lines B, which,
therefore, is not still satisfactory from the standpoint of reliably
preventing the inconvenience in that the upper part of the container
closure 1 inclusive of the top panel wall 7 is separated away from the
skirt wall 9 and jumps out. When the slanting angle θ is not
smaller than the above range, on the other hand, the aslant weakened
lines 30 are not easily broken. As a result, the pressure in the
container is strikingly elevated and should the breakage takes place, the
top panel wall 7 is broken over the whole circumference and may jump out.

[0100] Upon providing the weakened lines 63 which are aslant at a
predetermined angle θ as described above, the gas releasing
function can be enhanced as compared to when there are provided weakened
lines 60 extending in the axial direction, and the top panel jumping can
be prevented more reliably.

[0101] In the present invention, further, it is desired that the above
slanting angle θ is in a range of 10 to 30 degrees. That is, as the
slanting angle θ increases, the aslant weakened lines 63 become
less likely to be broken by the rise of the pressure in the container.
Therefore, as the slanting angle θ approaches 45 degrees, the
strength of the low-strength bridging portions 50a in the internal
pressure release line A must be decreased (width of the low-strength
bridging portions 50a in the circumferential direction must be decreased)
to quicken the breakage of these portions, so that the gas can be
reliably released by forming the opening 65 in case the pressure is
abnormally elevated in the container. However, if the width of the
low-strength bridging portions 50a is too shortened, the low-strength
bridging portions 50a tend to become easily broken at the time of
wrap-seaming the container closure 1 with the mouth-and-neck portion 70
of the container. Therefore, the allowable range becomes narrow in the
step of wrap-seaming, and precision is required for controlling the
wrap-seaming. When the slanting angle θ is considerably smaller
than 45 degrees and lies in a range of 10 to 30 degrees, the weakened
lines 30 break more easily than when the slanting angle θ is 45
degrees. Therefore, the width of the low-strength bridging portions 50a
does not need to be so shortened as that of when the slanting angle
θ is 45 degrees to decrease the strength. This broadens the
allowable range in the step of wrap-seaming, avoids the occurrence of
defective products, and is very advantageous for improving the
productivity.

[0102] In the present invention, further, it is desired to provide at
least one weakened line 67 extending in the axial direction for
accelerating the deformation between the pair of aslant weakened lines 63
formed at both ends of the internal pressure release line A. Upon forming
the weakened line 67, the skirt wall 9 is folded on the weakened line 67
for accelerating the deformation in case the aslant weakened lines 63 are
broken at both ends due to a sudden elevation in the pressure in the
container, and the skirt wall 9 easily and quickly deforms into a state
of being swollen outward, enabling the gas to be released more smoothly
and more quickly.

[0103] In the example of FIGS. 16 and 17, the pair of aslant weakened
lines 63 are extending upward and aslant at a predetermined slanting
angle θ. So far as the slanting angle θ lies in the
above-mentioned range, however, the aslant weakened lines 63 may extend
aslant in a direction in which they separate away from each other toward
the upper side as shown in a side view of FIG. 18 and in FIG. 19 which
illustrate a deformed state due to an elevated internal pressure. In such
a case, too, a large opening 65 of the shape of a beak is formed in the
internal pressure release line A due to the breakage of the aslant
weakened lines 63 or of the low-strength bridging portions 50a caused by
an abnormally elevated pressure in the container, and the gas is quickly
released through the opening 65 (see FIG. 19). From the standpoint of
preventing the top panel jumping, however, it is desired that the pair of
weakened lines are extending at a predetermined slanting angle θ in
a direction in which they approach each other from the lower side toward
the upper side. In this case, even when the breakage of the aslant
weakened lines 63 expands and spreads on the extensions thereof, the
breakage is in a direction to separate away from the internal pressure
release assist line B. The breakage does not proceed along the upper end
portion of the high-strong region B, and the top panel jumping is
prevented more reliably.

[0104] In the present invention, the pair of aslant weakened lines 63 can
be provided at both ends of the internal pressure release line A formed
by a long slit 20a which is extending in the circumferential direction
like the case of the weakened lines 60 in the axial direction described
above. In this case, too, the aslant weakened lines 63 extending at a
predetermined slanting angle (extending in this example in a direction in
which they approach each other toward the upper side) break due to an
abnormally elevated pressure in the container, whereby the slit 20a is
greatly torn forming a large opening 65 in the shape of a beak in the
internal pressure release line A as shown in FIG. 21 and enabling the gas
to be quickly released through the opening 65.

EXAMPLES

[0105] Excellent effects of the invention will now be described by way of
experiments.

[0122] There were provided containers made of a thin aluminum sheet having
a volume of 310 ml and a mouth-and-neck portion of a nominal diameter of
38 mm (outer diameter of the outer curling was 33.5 mm) placed in the
market from Mitsubishi Material Co., and the above container closures
were wrap-seamed with the mouth-and-neck portions of the containers as
shown in FIG. 4. Fifty container closures were wrap-seamed in quite the
same manner, but no breakage was at all recognized in the bridging
portions among the slits 20.

Experiment 2

[0123] Container closures were produced in the same manner as in
Experiment 1 but changing the specifications of the low-strength bridging
portions 50a in the internal pressure release line A of the container
closures as described below, and the wrap-seam testing was conducted in
the same manner.

[0127] As a result of wrap-seam testing, no breakage was recognized in the
bridging portions among the slits 20 in all of fifty container closures.

Experiment 3

Comparative Example

[0128] Container closures were produced in the same manner as in
Experiment 1 but without forming the annular bead, and the wrap-seam
testing was conducted in the same manner.

[0129] The pattern of arrangement of the slits 20 and the bridging
portions among them was quite the same as that of Experiment 1, and, for
example, the low-strength bridging portions 50a were as follows:

[0133] As a result of wrap-seam testing, breakage was recognized in the
low-strength bridging portions 50a among the slits of four container
closures out of fifty container closures.

Experiment 4

Comparative Example

[0134] Container closures were produced in the same manner as in
Experiment 1 but without forming the annular bead, and changing the
specifications of the low-strength bridging portions 50a forming the
internal pressure release line A of the container closure as described
below, and the wrap-seam testing was conducted in the same manner.

[0138] As a result of wrap-seam testing, breakage was recognized in the
low-strength bridging portions 50a among the slits 20 of one container
closure out of fifty container closures.

[0139] It will be learned from the above results that formation of the
annular bead makes it possible to effectively prevent the breakage at the
time of wrap-seaming even for the bridging portions have a small distance
among the slits 20.

[0140] That is, when the annular bead is formed as in the present
invention, it is allowed to form low-strength bridging portions having a
short distance among the slits 20, enabling the gas to be effectively
released even when the pressure is elevated little in the container. With
the container closure of Experiment 2, for example, the low-strength
bridging portions 50a were broken when the internal pressure was 0.86
MPa, and the gas was released.

[0141] With the container closure of Experiment 4 without forming the
annular bead, on the other hand, the bridging portions were broken for
the first time when the internal pressure was elevated to 0.97 MPa, and
the gas was released.

[0142] In the following Experiments, the strengths of the low-strength
bridging portions 50a in the internal pressure release line A were
measured as described below and were shown as vent bridge strengths (VS
strengths).

Method of Measuring the Vent Bridge Strengths:

[0143] Test pieces of a rectangular shape including two low-strength
bridging portions 50a of the inner side out of four low-strength bridging
portions 50a present in the internal pressure release line A were cut out
by using a pair of scissors from the aluminum container closures produced
in the above Experiments of before being wrap-seamed. Next, in a state
where the lower part of the test piece was fixed by using a fixing jig,
the upper part of the test piece was pulled up to measure the breaking
strength of the vent bridges in the axial direction by using a measuring
instrument (push-pull gauge).

Experiments 5 to 8

[0144] Container closures that can be wrap-seamed with threaded metal cans
having a mouth of a diameter of 38 mm were produced by using an aluminum
sheet of a thickness of 0.25 mm and a tensile strength of 215 N
manufactured by Sumitomo Light Metal Co.

[0145] The container closures that were produced possessed a structure as
shown in an expansion plan of FIG. 8 and, further, possessed aslant
weakened lines 63 extending aslant with respect to the axial direction at
both ends of the internal pressure release line A as shown in FIG. 16.

[0146] The aslant weakened lines 63 were so formed as to approach each
other toward the upper side by using such scores that left a thickness of
100 μm in the skirt wall 9. The aslant angles θ were selected to
be 10 degrees, 20 degrees, 30 degrees and 0 degree as shown in Table 1.
The samples were produced in a number of 10 for each Experiment.

[0147] The lines A to D that were formed possessed the following
specifications.

[0152] Bridging portions 50a: about 60 N of a total of two (width of about
0.60 mm per each bridge) [0153] Width of internal pressure release
assist lines C: 15 mm each

[0154] The aluminum container closures that were produced were treated
according to the procedure described below to prepare test samples.

(1) A threaded metal can (volume of 339 ml) made of aluminum manufactured
by Mitsubishi Material Co. was filled with hot water of 87±2°
C., and liquid nitrogen was added thereto dropwise to remove the air in
the head space, followed by capping. (2) The capped container was thrown
down sideways for 30 seconds and was, thereafter, erected upright. (3)
The container returned to the erected state was cooled by the shower of
water heated at 76° C. for 3 minutes, 50° C. for 5 minutes,
40° C. for 5 minutes and 35° C. for 5 minutes in this
order. (4) The container closure was opened by hand and, thereafter, the
cap was closed to the wrap-seamed position as in the initial state. (5) A
needle connected to a nitrogen feeding device was penetrated through the
body wall of the container in a test room at 23° C., and nitrogen
was supplied into the container at a rate of 0.034 MPa/s to elevate the
pressure in the container. (6) The pressure was measured in the container
with which the internal pressure release region was deformed and the
internal pressure was released.

[0155] At this moment, not only the number of deformations of the internal
pressure release regions A but also the number of breakage of the
container closures and the number of top panel walls that jumped, were
counted.

[0156] The results were as shown in Table 1.

Experiment 9

[0157] Test samples were produced in quite the same manner as in
Experiment 5 but selecting the slanting angle θ to be 45 degrees
and changing the vent bridge strength of a total of two low-strength
bridging portions 50a to be about 55 N, and were put to the experiment.
The results were as shown in Table 1.

TABLE-US-00001
TABLE 1
Experiment 5 Experiment 6 Experiment 7 Experiment 8 Experiment 9
θ
10° 20° 30° 0° 45°
Vent Jump- Vent Jump- Vent Jump- Vent Jump- Vent Jump-
No. pressure ing pressure ing pressure ing pressure ing pressure ing
1 0.80 no 0.76 no 0.85 no 0.82 no 0.71 no
2 0.79 no 0.75 no 0.88 no 0.81 yes 0.72 no
3 0.81 no 0.83 no 0.81 no 0.76 no 0.72 no
4 0.79 no 0.74 no 0.82 no 0.81 no 0.74 no
5 0.81 no 0.77 no 0.79 no 0.82 no 0.74 no
6 0.83 no 0.79 no 0.86 no 0.67 no 0.72 no
7 0.83 no 0.85 no 0.85 no 0.79 no 0.72 no
8 0.81 no 0.82 no 0.85 no 0.81 no 0.74 no
9 0.83 no 0.81 no 0.81 no 0.81 no 0.73 no
10 0.82 no 0.77 no 0.85 no 0.74 no 0.69 no
Ave. 0.812 *0/10 0.789 *0/10 0.837 *0/10 0.784 *1/10 0.723 *0/10
Max. 0.83 0.85 0.88 0.82 0.74
Min. 0.79 0.74 0.79 0.67 0.69
Vent pressure is a pressure of when the internal pressure is released and
is expressed in MPa.
*means jumping occurrences number.

Experiment 10

[0158] Container closures of the following specifications having lines A
to D in a pattern as shown in FIG. 8 were produced in the same manner as
in Experiment 1 by using the same thin aluminum base sheet as that of
Experiment 1.

[0173] There were provided containers made of a thin aluminum sheet having
a volume of 310 ml and a mouth-and-neck portion of a nominal diameter of
38 mm (outer diameter of the outer curling was 33.5 mm) placed in the
market from Mitsubishi Material Co. Each container was filled with 300 ml
of hot water of 85° C., and liquid nitrogen was added thereto
dropwise so that the pressure in the container was 0.13±0.05 MPa, and
the above container closure was wrap-seamed with the mouth-and-neck
portion of the container as shown in FIG. 4 to obtain a sample A.

[0174] Ten samples A were subjected to the compression test according to
the procedure described below. The container closure was, first, removed
by hand from the mouth-and-neck portion and was screw-fixed again to the
mouth-and-neck portion. Next, a needle having a gas-charging hole was
penetrated through the end of the top panel wall of the shell, and the
sample was submerged in the water vessel. The nitrogen gas was charged at
a rate of a pressure increase of 0.034 MPa/sec. to measure the internal
pressure with which the pressure in the container was released. A maximum
value was 0.93 MPa, a minimum value was 0.82 MPa and an average value was
0.88 MPa. The container closure mounted on the container from which the
internal pressure had been released was observed to find that the
low-strength bridging portions constituting the internal pressure release
line of the shell had been broken and that the top panel wall of the
shell and the liner arranged in the inner surface thereof had been
deformed.

[0175] Further, ten samples were subjected to the 30-cm drop impact test
according to the procedure described below. First, the pressure in the
container was measured through the body wall of the container by using
the "Non-Destructive Pressure-in-the-Can Measuring Instrument" placed in
the market from Daiwa Seikan Co. Next, the container in an inverted state
was allowed to freely fall 30 cm vertically through a falling passage,
and the portion of the low-strength region constituting the internal
pressure release line was allowed to come into collision with a steel
cylindrical member of which the upper surface was aslant by 10 degrees.
After left to stand 24 hours (a whole day), the pressure in the container
was measured by using the above "Non-Destructive Pressure-in-the-Can
Measuring Instrument" to find that there was no decrease in the internal
pressure (i.e., no leakage has occurred).